we bought a home with an unfinished basement that has failrly rough floors. we'd like to stain the concrete; but, obviously, the first step is to determine how much of a task it'll be to smooth out the concrete. some spots aren't so bad, and other spots have some lines that were left from when the concrete was poured. how do i know how much i need to grind the floors down, or do i try to polish it first? i've got 2100 sq. ft. of basement; is it feasible to do this job on my ownwith a rental grinder?